Perovskites carbonate composite

A covalent model has been provided to explain the limiting range of carbon composition and the possible structure of the R3SnC t compounds (McColm et al. 1971). The perfect perovskite carbide structure would have a carbon atom in the octahedral site at the center of the unit cell. However, a random distribution of lanthanide and tin atoms occurs over all the fee sites. In this situation, a probability... 

Amar, I. A., Petit, C. T. G., Zhang, L., Lan, R., Skabara, P. J., Tao, S. W. (2011). Electrochemical synthesis of ammonia based on doped-ceria-carbonate composite electrol3fte and perovskite cathode. Solid State Ionics, 201, 94—100. 

Barium carbonate also reacts with titania to form barium titanate [12047-27-7] BaTiO, a ferroelectric material with a very high dielectric constant (see Ferroelectrics). Barium titanate is best manufactured as a single-phase composition by a soHd-state sintering technique. The asymmetrical perovskite stmcture of the titanate develops a potential difference when compressed in specific crystallographic directions, and vice versa. This material is most widely used for its strong piezoelectric characteristics in transducers for ultrasonic technical appHcations such as the emulsification of Hquids, mixing of powders and paints, and homogenization of milk, or in sonar devices (see Piezoelectrics Ultrasonics). 

Barium titanate is usually produced by the soHd-state reaction of barium carbonate and titanium dioxide. Dielectric and pie2oelectric properties of BaTiO can be affected by stoichiometry, micro stmcture, and additive ions that can enter into soHd solution. In the perovskite lattice, substitutions of Pb ", Sr ", Ca ", and Cd " can be made for part of the barium ions, maintaining the ferroelectric characteristics. Similarly, the TP" ion can partially be replaced with Sn +, Zr +, Ce +, and Th +. The possibihties for forming solution alloys in all these stmctures offer a range of compositions, which present a... 

Some ceramic materials are not found widely or at all in nature, and thus are synthesized for use. To prepare more complex ceramic compositions such as perovskites of general structural formula ABO3, and ferrites, of formula MFc204, the individual oxides or salts of the cations A, B, and M are often combined as powders and then reacted at high temperature by a solid-state diffusion mechanism. Silicon nitride (Si3N4) can be manufactured from either the nitridation of silicon metal or from the reaction of silicon tetrachloride with ammonia. Silicon carbide (SiC) is obtained from the reduction of silica with a carbon containing source. 

A series of perovskite compositions were synthesized using oxides and carbonates of the cations by conventional ceramic process. The synthesized powders were characterized using powder x-ray diffraction technique to ensure phase purity. Conductivity measurements were made in H2-H2O atmosphere to determine proton conductity. As the perovskite compositions are inherently mixed conducting, the transference numbers for proton and electron conduction were also determined by varying the partial pressures of hydrogen and steam across the membrane. 

Two compositions of the composite materials were evaluated for stability in syngas. Sintered pellets of the composite were crushed to powder form to increase the surface area of the material. The powdered composites were exposed to syngas at 900°C for 4 hours. A baseline perovskite composition was also exposed to similar conditions. X-ray diffraction analysis of the materials is shown in Fig. 4.5. As can be seen, while the baseline perovskite readily formed a carbonate phase, the composite materials showed significantly improved stability in syngas. 

The compounds R3MC and RM3C3 are the only known compositions that exist in the rare-earth-metal-(aluminium, gallium, indium and thallium)-carbon systems at the present time. A number of reports on the preparation of cubic perovskite-type carbides containing rare earth elements with the general formula RjMC 00 (Jeitschko et al. 1964, Rosen and Sprang 1965, Haschke et al. 1966a, b, Nowotny 1968) contain little information about their properties other than their lattice parameters. 

To this end, I invited an international team of highly expert scientists from the field of membrane science and technology to write about the state-of-the-art of the various kinds of membranes (polymeric, Pd- and non-Pd-based, carbon, zeolite, perovskite, composite, ceramic and so on) used in membrane reactors, modelling aspects related to all kinds of membrane reactors, the various applications of membrane reactors and, finally, economic aspects. 

Rosa et al. [251] set up a complete 5-kW diesel fuel processor based on autothermal reforming and catalytic carbon monoxide clean-up, which was dedicated to a low temperature PEM fuel cell. The breadboard system was composed of the autothermal reformer operated between 800 and 850 °C with a ruthenium/perovskite catalyst (see Section 4.2.8), a single water-gas shift reactor containing platinum/titania/ceria catalyst operated between 270 and 300 °C (see Section 4.5.1), and a preferential oxidation reactor containing platinum/alumina catalyst operated between 165 and 180 °C. Figure 9.54 shows the gas composition and reactor temperatures achieved. The hydrogen content of the reformate was in the range from 40 to 44 vol.% on a dry basis. The carbon monoxide content of the reformate was 7.4 vol.% and could be reduced to values of between 0.3 and 1 vol.% after the water-gas shift reactor and to below 100 ppm after the preferential oxidation reactor. 

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